In recent years, the need to further enhance the performance and reduce the size of electronic products has become stronger than ever before, and with this trend, the need for a smaller, lighter, higher capacity, and a higher energy density device has also been increasing in the field of materials for batteries that provide energy for such electronic products. Therefore, various research and development has taken place. To meet such needs, solid electrolytes have been attracting attention in recent years as new ionic conductors which are expected to replace conventional electrolytic solutions, and applying solid electrolytes to electrochemical devices such as all-solid primary batteries, secondary batteries, and capacitors has been tried. Electrochemical devices using conventional electrolytic solutions have safety and reliability problems because of solution leakage and solute seeping. Extensive studies are under way on so-called polymer electrolytes which use a polymer compound as the electrolyte in order to overcome the shortcomings associated with conventional electrolytic solutions. Polymer electrolytes are flexible and are able to conform to deformation caused by a mechanical impact or a change in electrode volume that occurs in relation to an ion-electron exchange reaction taking place between the electrode and the electrolyte. As an example of such a polymer electrolyte, U.S. Pat. No. 4,303,748 proposes a solid electrolyte produced by dissolving an alkali metal salt or an alkaline earth metal salt in polyalkylene oxide, but this solid electrolyte decreases in productivity as it takes time to dissolve the salt, and also ionic conductivity is not sufficient and contact resistance with the electrode material is high. When the ionic conductivity is not sufficient, and the contact resistance is high, a sufficient charge/discharge current density cannot be obtained, and the range of applications of the electrolyte is limited because it cannot be used in applications where a large current is required.
To overcome the shortcoming of the above solid electrolyte, there have been proposed a variety of solid electrolytes, each produced by dissolving an alkali metal salt or an alkaline earth metal salt in a polymer that has poly(metha)acrylate as the backbone and polyalkylene glycol chains as the side chains and/or crosslinking chains. One such polymer electrolyte is the solid electrolyte proposed in Japanese Examined Patent Publication No. H03-73081, which is produced by dissolving an alkali metal salt or an alkaline earth metal salt in an acryloyl-modified polyalkylene oxide, but this electrolyte still results in insufficient ionic conductivity and the mobility of cations that contribute to charging and discharging being low. When the ionic conductivity is not sufficient, and the mobility of cations is low, a sufficient charge/discharge current density cannot be obtained, and the range of applications of the electrolyte is limited because it cannot be used in applications where a large current is required, and because the movement of counter-anions may produce an undesirable secondary reaction, degrading the electrolyte as the charge/discharge cycle is repeated. To control the movement of ions that can contribute to charging and discharging in the polymer electrolyte composed principally of a ring-opening polymerization product of such alkylene oxide derivatives, Japanese Unexamined Patent Publication Nos. H11-54151 and 2001-55441 each propose an electrolyte formed from a tri-functional boron compound such as a boroxin ring that captures the counter-anions of the metal salt. Further, to enhance the ionic conductivity, Japanese Unexamined Patent Publication Nos. 2001-155771, 2001-273925, 2002-158039, and 2002-334717 each propose an electrolyte formed from a compound containing boron. However, orthoboric acid or boron oxide is used as a boron-containing compound used to obtain such compounds, and water is produced by desorption during the reaction with the compound. Furthermore, the obtained compound can be easily hydrolyzed with water, making it extremely difficult to remove the produced water. As a result, the presence of water in the resulting compound is unavoidable, and this may present a problem when using the compound as the electrolyte base material. Japanese Unexamined Patent Publication Nos. 2001-72876 and 2001-72877 also propose an electrolyte formed from a compound containing boron, but borane is used as the source of boron used to obtain the compound. However, since borane, which is a compound represented by BnHm, is highly reactive and spontaneously flammable in air, it is difficult to handle the material during manufacturing of a boron-containing compound, and when it is used in a reaction with a compound having a polymerizable group, the polymerizable group may be damaged. To solve the problems associated with the use of such boron-containing compounds, Japanese Unexamined Patent Publication No. 2003-201344 proposes to use a boric acid ester as a boron-containing compound and to manufacture a boric acid ester compound using a boric acid ester exchange reaction.